Clutch module with predetermined torque

ABSTRACT

A field installable motor operator for a circuit breaker includes a bidirectionally controllable motor that is coupled through a torque limited module to a circuit breaker operating mechanism. The motor is bidirectionally driven by a transistor switching bridge that supplies output current in reversible flow directions through one of the windings of the motor to the input of a rectifier bridge that supplies the other winding with currents that flow in the same direction. The torque limited module includes a centering and spacing ring which precisely confines the clutch elements to provide consistent torque. The motor is supplied with a current pulse of 250 milliseconds duration that is longer than the time required to fully operate the breaker. The clutch slips when breaker opeation is completed and permits the motor to overrun without damage.

CROSS REFERENCE TO RELATED APPLICATIONS:

This application discloses apparatus claimed in copending applicationsSer. No. 316,849, filed Feb. 28, 1989, entitled Field InstallableElectrical Operator For A Circuit Breaker, in the names of R. Etscheidt,D. Ophaug and H. Zylstra, and Ser. No. 317,268, filed Feb. 28, 1989,entitled Electronic Control Circuit for a Bidirectional Motor in thenames of H. Zylstra and R. Etscheidt, all of which are assigned toSquare D Company.

BACKGROUND OF THE INVENTION AND THE PRIOR ART:

This invention relates generally to motorized operators for circuitbreakers used on electrical power systems and the like and specificallyto electrical operators for such mechanically operated circuit breakersthat may be readily installed on site, i.e. in the field.

One of the principal advantages of having the capability of electricallyopening and closing circuit breakers is the ability to remotely operatethe breaker in response to operator control as well as in response tofault currents. With electrically controlled motorized systems foropening and closing the circuit breakers, load switching and branchcircuit protection may be rapidly and effectively accomplished becauseof the elimination of the need for a technician to physically manipulatethe operating mechanism of the circuit breaker.

In many instances, it is desirable to upgrade a mechanically operatedbreaker by installing a motor control system therefor. Most of the motorcontrol systems include mechanical electric switches to run thebidirectional motor in addition to limit switches for stopping the motorwhen the breaker reaches an operating position, i.e. either fully openedor fully closed. It is desirable to open or close a breaker rapidly andthe limit switches, especially, are difficult and awkward to adjust inthe field, and may be adjusted improperly.

As alluded to above, it is desirable that the circuit breaker operate toopen or close all electrical phases as rapidly as possible and within aminimum time period for all phases. The motor drive must thereforerapidly start the motor, deliver very high torque for approximately 105degrees of angular rotation, and rapidly stop. These severe requirementshave necessitated the use of expensive apparatus that requires carefuladjustment.

The present invention is directed to a novel torque limited module thatmay be used to couple a bidirectional high torque motor to the operatingmechanism of a multiphase circuit breaker through a single reductiongear. The torque limited module includes a clutch that is centered on adrive shaft and precisely loaded by means of a centering and spacingring in the form of a cylinder. An upper and lower module plate embracesthe spacer ring, which houses all of the clutch elements. A pair ofBelleville washers load the clutch and a pair of friction discs,separated by a spacer ring, increases the clutch frictional force. Thespacer serves to increase the surface area of friction slippage andimproves the operation of the clutch. This torque limited module permitsthe motor to overrun the breaker operation, i.e. the motor runs for ashort time after the breaker has been fully operated, that is opened orclosed. The field installable electrical operator and the electronicmotor control systems are individually the subjects of the abovementioned copending applications since they have separate utility apartfrom the present invention.

OBJECTS OF THE INVENTION:

A principal object of the invention is to provide a novel torque limitedmodule.

Another object of the invention is to provide an improved clutchapparatus that is readily assembled and consistent in its loading.

A further object of the invention is to provide a clutch apparatus thatdoes not require adjustment.

BRIEF DESCRIPTION OF THE DRAWINGS:

These and other objects and advantages of the invention will be apparentupon reading the following description in conjunction with the drawingsin which:

FIG. 1 is a simplified block diagram of an electrical operatorconstructed in accordance with the invention;

FIG. 2 is a plan view of a circuit breaker having the electricaloperator of the invention installed thereon;

FIG. 3 is a perspective view of the motor, torque limited module housingand indicator plate;

FIG. 4 is an enlarged exploded view of the clutch elements and thetorque limited module;

FIG. 5 is a reduced partial view, taken along the line 5--5 of FIG. 4,illustrating the drive arrangement between the motor and the torquelimited module and the clutch mechanism;

FIG. 6 is a partial view showing the assembled torque limited module andclutch elements;

FIGS. 7 through 11 are reduced sectional views taken along the lines 7through 11, respectively, of FIG. 4;

FIG. 12 is a simplified illustration of the bidirectional motor supplysystem;

FIG. 13 illustrates the relationship between the control signal and thetimed motor current;

FIG. 14 is a more detailed diagram of the bidirectional motor supplysystem;

FIG. 15 illustrates the control signal input, opto coupler output andfixed duration motor drive current for the electronic motor controlsystem; and

FIG. 16 is a detailed schematic diagram of the electronic motor controlsystem.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1 a block 10, labelled Motor and Control Circuit is suppliedwith a control signal, resulting in rotation of a motor shaft 11 that iscoupled to a block 12, labelled Torque Limited Module. The torquelimited module 12 has an output drive shaft 13 that is coupled to ablock 14, labelled Circuit Breaker, for angularly rotating the operatingmechanism arms of the circuit breaker through a limited angle foropening (or closing) electrical circuits completed therethrough.

In FIG. 2 a plan view of circuit breaker 14 is illustrated with itsprotective door removed to show the electrical operator in position. Ahousing 15 encloses the circuit breaker elements. Six electrical lugs 16protrude from the top and the bottom of the housing 15 and are adaptedfor connection to appropriate circuits (not shown). The end of driveshaft 13 is seen to have opposed flat sides giving it a familiar doubleD shaped cross section. A motor 17 is coupled to a module housing 23which includes a torque limited module that rotates drive shaft 13. Anindicating disc 18 is mounted in a fixed position to the end of driveshaft 13 to indicate the operated condition of the breaker, i.e. whetherit is ON or OFF. A mounting plate 25 is provided for securing motor 17and module housing 23 in proper position on breaker 14. An elongated box20, mounted on mounting plate 25 adjacent to motor 17, includeselectronic control circuitry for controlling operation of motor 17 basedupon appropriate open and close control signals which are appliedthrough the indicated cabling at 20a. It will be appreciated that theelectrical operator breaker door or cover, which is not illustrated and,which encloses mounting plate 25 includes a suitable viewing aperture sothat the legend ON or OFF is visible therethrough to indicate theoperational position of the circuit breaker, i.e. whether ON or OFF. Apush button ON/OFF switch may also be mounted on the mounting plate 25or on housing 15 to enable a technician to operate the circuit breakerat the premises. As will be seen, the shaft of motor 17 may bemechanically turned by a screw driver or other similar tool to"manually" operate the circuit breaker through the reduction gearing.Naturally, a number of revolutions of the motor armature are required tooperate the breaker. While not illustrated, the breaker operatingmechanism includes a handle that is removed when installing a motorizedoperator. A suitable adapter is placed on the end of the breakeroperating shaft, which is engaged by the drive shaft of the electricaloperator mechanism, as will be seen. The illustration is for a breakerwith a front mounted rotatable operating handle, but with suitablemodifications the system is readily adaptable for use with side mountedbreaker handles.

In FIG. 3 the motor 17, module housing 23 and indicator plate 18 areshown in perspective. The base of the motor includes an access opening17a in which a screw driver may be inserted for engaging a slot in theend of the motor armature shaft (not shown) to permit rotation of themotor armature shaft to operate the breaker in the event of a failure inthe electrical control system. A mounting base 22 serves to affix motor17 and module housing 23 to mounting plate 25 by the use of suitablefasteners. A removable module housing cover 24 enables access to thetorque limited module and clutch elements (and gears) enclosed in modulehousing 23. The flat portions 13a on the indicator plate end of driveshaft 13 engage a similarly shaped aperture in indicator plate 18. Acircular spring clip 19 in a groove on the end of shaft 13 securesindicator plate 18 in position on the end of drive shaft 13. Any othersuitable fastener arrangement may be used, however. The breakeroperating end of drive shaft 13 with flat portions 13c is also visible.

FIGS. 4, 5 and 6 show the various portions of the torque limited clutchmodule 12, and the clutch elements. Referring specifically to FIG. 4,drive shaft 13 is seen to have flat portions 13a, 13b and 13c formingdouble D cross sections. An annular groove 21 in the end of drive shaft13 adjacent flat portions 13a, cooperates with the clip 19 (FIG. 3) forretaining indicator plate 18 in position. It will be appreciated that atop bearing and supporting element for positioning drive shaft 13 in themodule housing cover 24 is omitted for clarity in FIG. 4.

The clutch elements and the torque limited module, shown in explodedview, are enclosed within the bracket 12'. The torque limited module 12is bounded by an upper module plate 26 and a lower module plate 28. Themodule plates are secured by a plurality of circularly disposed screws27 which pass through appropriate holes in upper module plate 26 andinto threaded apertures 29 in lower module plate 28. An annularcentering and spacing ring or cylinder 30 is disposed adjacent theunderside of upper module plate 26. The clutch elements comprise a pairof annular friction discs 32 and 34 which are separated by a thinannular spacer disc 36 and a clutch drive plate 38. It will be notedthat the upper module plate 26, friction disc 32, spacer disc 36 andfriction disc 34 have central openings 31a, 31b, 31c and 31drespectively, of larger diameter than the diameter of the portion ofdrive shaft 13 in the area of flat portions 13b above a shoulder 44.Clutch drive plate 38, differs however, and has a double D shapedopening that matches the cross section of drive shaft 13 at flatportions 13b, which locks the clutch drive plate 38 to drive shaft 13.The clutch drive plate 38 therefore rotates with drive shaft 13. A pairBelleville of springs or washers 40 complete the torque limited module.Lower module plate 28 has a larger double D shaped opening with flatsides 49 that engage a similarly shaped shoulder 48 formed at one end ofa drive gear 42. Drive gear 42 is freely rotatable on drive shaft 13. Asindicated by the dashed line circle, a pinion gear 46 on the end ofmotor shaft 11 engages the gear teeth 51 about the periphery of drivegear 42.

As best seen in FIG. 5, motor shaft 11 has its end terminating in piniongear 46 that engages teeth 51 about the circumference of drive gear 42.A suitable bearing support 45 supports drive gear 42 at the end of driveshaft 13 adjacent to the circuit breaker. The torque limited module 12and other supporting structure (not shown), engaging shaft 13, keepdrive gear 42 in contact with bearing support 45. The flat side portions13c at the lower end of drive shaft 13 present a double D shaped crosssection fits into a breaker adapter 52, generally indicated by arectangle. Breaker adapter 52 has a suitable mating recess 53 fordriving engagement with the lower end of drive shaft 13 (at 13c). Ascrew or other suitable fastener 54 affixes breaker adapter 52 to theend of breaker operating mechanism 56. As mentioned, when the motorizedoperator is to be used, the circuit breaker operating handle is removedand adapter 52 is installed in its place. The configuration of thevarious parts depends upon the shape and arrangement of the breakeroperating mechanism and the breaker housing and consequently only ablock diagram representation of such parts is included. As indicated,the drive shaft 13 protrudes through an orifice in mounting plate 25 topermit driving engagement with breaker adapter 52. A bearing member 58rotatably supports drive shaft 13 where it extends through modulehousing 23.

FIG. 6 illustrates the assembled torque limited module and clutchwherein the various elements are squeezed together between the upper andlower module plates, by virtue of the spring force of Belleville washers40 and tightening of screws 27, to fit wholly within the confines ofcentering ring or cylinder 30. The upper portion of drive shaft 13passes through another bearing 47 and the top of module housing cover24. Centering ring 30 serves as a stop for the upper and lower moduleplates 26 and 28, respectively. During assembly of the torque limitedmodule, screws 27 are drawn up tight thus forcing all of the elementswithin the confines of cylinder 30. As a result, cylinder 30 not onlyserves to maintain the various clutch elements in alignment, itestablishes a consistent torque load for the clutch and which may beconveniently assembled at a remote location until ready forinstallation. Hence the name torque limited module.

As shown in FIGS. 7 through 11, the upper module plate 26 includes acentral hole 31a of larger diameter than the diameter of the upperportion of drive shaft 13. Also shown are screws 27 circumferentiallydisposed about the upper module plate to facilitate securing theelements of the assembly. The top view of the centering ring 30 in FIG.8 shows its cylindrical construction. The friction discs 32 and 34 ofFIG. 9 have a slightly smaller outer diameter than the inner diameter ofcylinder 30 and have a central hole 31b having an inner diameter thatenables the drive shaft 13 to freely pass therein. The spacer disc 36 isnot illustrated but has the same shape as the friction discs 32 and 34.The purpose of the spacer disc is to double the clutch's frictionalsurface to provide improved loading effect. The clutch drive plate 38 inFIG. 10 includes a plurality of optional spaced holes 41 for aiding indistribution of grease between the various clutch elements andcollection of eroded friction disc material. It also has a double Dshaped cutout having flat portions which engage the flat sides 13b ofdrive shaft 13. Therefore the clutch drive plate 38 is rotatable withdrive shaft 13 at all times. The lower module plate 28 shown in FIG. 11includes a larger double D shaped cross section having a pair of flatsides 49 for cooperative engagement with a similarly shaped shoulder 48on gear wheel 42. A plurality of threaded holes 29 receive screws 27 forsecuring the torque limited module assembly together.

Operation of the torque limited module is straightforward. All of theclutch elements, with the exception of drive plate 38, are freelymovable on drive shaft 13. By virtue of the force imposed by Bellevillesprings 40 on the clutch elements (which are captivated between theupper and lower module plates) frictional drive forces are developedbetween: the under side of upper module plate 26 and the upper side offriction disc 32; the under side of friction disc 32 and the upper sideof spacer disc 36; the under side of spacer disc 36 and the upper sideof friction disc 34; and the under side of friction disc 34 and theupper side of clutch drive plate 38. The interior of module housing 23is filled with a suitable grease for lubrication and heat dissipationpurposes and the friction discs and Belleville springs are selected todevelop approximately 55 lb-ft of torque. For loadings beyond that, thefriction elements slip and rotation of gear wheel 42 (by pinion gear 46)does not result in rotation of drive shaft 13. For loads less than thatfor which the torque limited module is made to slip, rotation of gearwheel 42 causes rotation of drive plate 38 and drive shaft 13. When thecircuit breaker operating mechanism reaches its fully open or fullyclosed position, the load imposed on drive shaft 13 becomes greater thanthe slip force for the torque limited module and the clutch slips topermit the motor to overrun without causing damage.

FIG. 12 illustrates general operation of the motor controlled circuitbreaker system. A timer driver block 50 having control signal inputs Aand B (A representing clockwise motor rotation and B representingcounter clockwise rotation), selectively operates two pairs of switchesin a switching bridge 57 for providing oppositely directed currents to amotor 55 for causing bidirectional rotation as indicated by the arrows.Motor 55 is coupled to the individual electrical phase connectors inthree-phase circuit breaker 14. The switch bridge 57 terminals arearbitrarily marked 70, 71 and 72, 73 to indicate input terminals andoutput terminals, respectively. In accordance with the invention, apredetermined duration drive current or drive pulse is supplied to motor55. The energy supplied is sufficient to assure complete opening (orclosing) of the mechanical elements in circuit breaker 14, with thetorque limited module accommodating motor overrun.

As indicated in FIG. 13, an input control signal may comprise a pulse 59of limited duration. The dashed line trailing the end of pulse 59indicates that the pulse may have a longer duration. Indeed, in thepreferred implementation, the input signal may be continuous AC or DC.The motor current that flows in response to the input control signal isa fixed quantity 61, indicated by the current 61 bearing the legendTIMED. The shaded portion near the end of 61 indicates the torquelimited module slip time during which the motor continues to run afterthe breaker has been fully operated.

FIG. 14 shows an enlarged view of a double bridge arrangement forbidirectionally controlling the motor. The motor has two separatewindings, M1 and M2 which may comprise conventional armature and fieldwindings. The switching bridge input terminals 70 and 71 are connectedbetween voltage V and ground. The arms of switching bridge 57 constitutetwo parallel paths of series-connected switches Q1, Q2, Q3 and Q4, withQ1 and Q4 being identified as the B or counterclockwise rotationswitches, and Q2 and Q3 being identified as the A or clockwise rotationswitches. The switches identified as Q1-Q4 correspond to the similarlyidentified transistors in FIG. 16. The M2 motor winding has one endconnected to the output terminal 73 of the switching bridge 57, definedby the junction of Q2 and Q4, and its other end connected to an inputterminal 80 of a rectifier bridge CR1, comprising four diodes D1-D4, theother input terminal 81 of which is connected to the output terminal 72of the switching bridge 57. Output terminal 72 is defined by thejunction of Q1 and Q3. The output terminals 82 and 83 for the rectifierbridge CR1 are connected to winding M1. As indicated, in response toclosure of switches Q2 and Q3, an A current flows (as indicated by thearrow) from left to right through winding M2 and from top to bottomthrough winding M1. In response to closure of switches Q1 and Q4, a Bcurrent flows from top to bottom through winding M1, and from right toleft through winding M2. As the duration of current flow in winding M2is reversible, whereas the current in winding M1 always flows in thesame direction, the motor will run in opposite directions, in responseto closure of switches Q2 and Q3 and to closure of switches Q1 and Q4,respectively. An important feature of the control circuit is that nomechanical switches are required, with Q1-Q4 being the emitter-collectorjunctions of transistors. This operation contrasts with the prior artcontrol circuits incorporating mechanical reversing switches and limitswitches with consequent heavy contact wear and need for isolation dueto the switched inductive motor currents.

In FIG. 15, the C curve indicates control input current based upon an ONor OFF control signal 85 and Curve D represents the timed motor drivecurrent and the torque limited module slip operation as indicatedpreviously.

Referring to the schematic diagram of FIG. 16, AC line power is appliedto pins 1 and 3 of an input plug P1, through a fuse F, to pins 2 and 3of a full wave bridge rectifier CR2. A MOV, identified as VR1, iscoupled across the AC line and serves to limit the applied voltage. Theoutput from pin 1 of rectifier CR2 is applied to a resistor R4 throughan electrolytic capacitor C7 to ground. A zener diode CR7 is coupledacross capacitor C7 and together these elements provide preregulationfor a low voltage regulator U2, which supplies VCC potential. Therectified current from CR2 is coupled to junction 70 which is the inputterminal of the switching bridge 57 discussed in FIGS. 12 and 14. Theemitters of a pair of transistors Q5 and Q6 are connected to junction70, as are the collectors of a pair of switch transistors Q1 and Q2. Apair of resistors R6 and R5 connect the emitters of transistors Q5 andQ6 to their respective bases. A MOV VR4 is connected from junction 70 toground to further protect the circuitry from excessive voltage. Theemitter of switch transistor Q2 is connected to the collector of aswitch transistor Q4 whose emitter is connected to ground. The base ofswitch transistor Q4 is connected to ground through a resistor R7.

Resistor R5 is connected to a resistor R2 and their junction isconnected to the base of transistor Q6. The collector of transistor Q6is connected to the base of switch transistor Q1. The other end of R2 isconnected to the drain (D) of an FET Q8 having a grounded source (S)electrode. The gate (G) of FET Q8 is connected to the gate of an FET Q9and through a resistor R9 to ground. D of Q9 is connected through aresistor R28 to the emitter of switch transistor Q1 and to the collectorof a switch transistor Q3 having a grounded emitter. S of Q9 isconnected to R7. The base of transistor Q5 is connected to the junctionof resistor R6 and a resistor R3, which is connected to D of FET Q10. Sof Q10 is grounded. G of Q10 is connected to the gate of an FET Q7 andthrough a resistor R10 to ground. S of Q7 is connected to ground througha resistor R8 and to the base of switch transistor Q3. D of Q7 isconnected through a resistor R1 to output terminal 72 of the switchingbridge 57 and to input terminal 81 of the rectifier bridge CR1. Outputterminals 82 and 83 of rectifier bridge CR1 are connected to the M1motor winding, across which is coupled a diode CR11. The input terminal80 of rectifier bridge CR1 is connected to the M2 winding of the motorwhich is returned to output terminal 73 of switching bridge 57. Theabove described circuitry corresponds to the illustration in FIG. 14,with the transistors Q1-Q4 being part of the switching bridge 57 and thediodes D1-D4 comprising the rectifier bridge CR1.

The gates of FETS Q8 and Q9 are coupled, through a resistor R11, toterminal 6 of a timer U1, and the gates of FETS Q7 and Q10 are coupled,through a resistor R12 to pin 10 of timer U1. U1 is a dual monostabletimer available as part No. CD4098 from a number of electronicsmanufacturers. The pin numbers indicated correspond to those marked onthe actual device. A pair of opto couplers, U3 and U4, identified aspart Nos. 4N37 are used to provide isolation between the input signalcircuitry and the control signal circuits. A capacitor C11 is connectedacross pins 1 and 2 of opto coupler U4, pin 4 is grounded and capacitorsC13 and C15 connect pins 5 and 6 to ground, respectively. Pin 5 of U4 isalso coupled to VCC through a resistor R17. VCC is applied through theparallel arrangement of a resistor R18 and a reverse connected diodeCR3. A capacitor C6 couples pin 5 of U4 to pin 5 of U1.

The opposite input opto coupler U3 has its pin 6 connected to groundthrough a capacitor C14. Pin 5 is similarly connected to ground througha capacitor C12, and pin 4 is grounded. A capacitor C10 is coupledacross pins 1 and 2. VCC is applied through R15 to pin 5 of U3 andthrough parallelly coupled R16 and reverse connected diode CR4 to pin 11of U1. A capacitor C5 couples pin 5 of U4 to pin 11 of U1.

Pin 4 on an input plug P1 is connected through a diode CR8 and a seriesconnection of resistor R24 and resistor R22 to pin 1 of U3. Similarlyinput pin 5 is connected through a diode CR9 and resistors R23 and R21to pin 1 of U4. The junction of C11, C9 and CR6 is connected to thejunction of C10, C8 and CR5 and to input pin 2 of plug P1 through adiode CR10. A pair of switches 61 and 62 are operated by a controlsignal block 60 to selectively connect pins 2 and 4, and pins 2 and 5together through respective DC sources 63 and 64, indicated forsimplicity as batteries. A pair of MOVs VR2 and VR3 protect the inputpins from excessive voltages. The duration of the output currents fromU1 is controlled by the combinations of capacitor C1 and resistor R13and capacitor C2 and resistor R14, respectively, each of which iscoupled to VCC. In the preferred embodiment of the invention, the pulseduration is established at 250 milliseconds, which is a time sufficientto insure complete breaker operation for the class of circuit breakerswith which the electrical operator of the invention is used.

The timer U1 is precluded from responding to successive input controlsignals by virture of transistors Q11 and Q12. Transistors Q11 and Q12have their emitters connected to ground, and their collectors connectedto VCC through resistors R30 and R29, respectively. R29 and R30 arebypassed to ground via capacitors C3 and C4 respectively. The collectorof Q11 is connected to pin 13 of U1 and its base is connected through aresistor R25 to pin 6 of timer U1. The collector of Q12 is connected topin 3 of U1 and its base is connected through a resistor R26 to pin 10of U1.

In operation, closure of switch 61 or 62, in response to an appropriatecontrol signal from control signal block 60, results in either pin 5 orpin 11 of timer U1 being brought to a low logic level. In response topin 5 going low, an output pulse is produced at pin 6. Similarly, inresponse to pin 11 going low, an output pulse is produced at pin 10. Thelength of the output pulses, as mentioned, is determined by R14 and C2for the pulse from pin 6 and by R13 and C1 for the pulse from pin 10.When switch 61 is closed, the motor will be driven in a clockwisedirection and when switch 62 is closed, the motor will be driven in acounter clockwise direction. The positive input signals, coupled viaswitches 61 and 62 to pins 4 and 5 respectively of connector P1, turn ontransistors (not shown) in opto couplers U3 and U4 respectively.Currents to the opto coupler diodes are limited by resistors R21 andR23, for device U4, and by resistors R22 and R24 for device U3. Thezener diodes CR5 and CR6 limit the input signal voltages and thereforethe opto coupler currents. The capacitors C8 and C9 provide noisesuppression and also provide sufficient storage to allow operation witheither AC or DC control signals. A control signal saturates the optocoupler transistors, resulting in their collectors falling to nearground potential. This change in voltage level is coupled to pins 5 and11, respectively of timer U1 to thereby initiate the drive pulses. Itwill be appreciated that only one of opto couplers U3 and U4 issaturated at any given time, depending on which of the input switches 61or 62 is closed. The capacitors C5 and C6 immediately charge throughrespective resistors R16 and R18 and apply VCC potential to pin 5 andpin 11, respectively.

To prevent an output current pulse tending to drive the motor in aclockwise direction and an output current pulse tending to drive themotor in a counter clockwise direction simultaneously, and to insuredevelopment of only a single output current pulse in response to acontrol signal, the reset lines of the monostable U1 are cross coupled.The output of U1, pin 10 is applied to Q12 through resistor R26 and thecollector of Q12 is connected to pin 3 of U1. Pin 3 is the reset linefor the other timer section of U1. Similarly the output of pin 6 of U1is applied to the base of Q11 through R25 and the collector of Q11 isconnected to pin 11 of U1 which is the reset line for the opposite timersection of U1. When a reset line is held low, it prevents an outputpulse current from that particular timer section. Consequently with thecross coupling of the timer sections, the timer will only deliver asingle pulse for a single actuation of its corresponding switch 61 or62. Effectively the timer sections are toggled and only a single outputcurrent is produced despite repeated or continuous application of acontrol signal.

The transistors Q1-Q10 and the rectifier bridge CR1 providebidirectional drive currents to the motor armature and field windings M1and M2 for precisely controlled time periods. For clockwise rotation,FETs Q7 and Q10 receive a drive pulse of approximately 250 millisecondsfrom pin 10 of timer U1. FETs Q7 and Q10 are driven conductive andprovide a low resistance path to ground. FET Q10, in turn, provides basedrive for transistor Q5 through R3, which results in transistor Q5turning on. The collector current of transistor Q5 provides base drivefor transistor switch Q2, which together with switch Q3 controls theflow of motor current. FET Q7 provides base drive for switch transistorQ3 via resistor R1. Switch transistor Q3 in conjunction with Q2 controlsthe motor current for rotation in a clockwise direction.

In the counter clockwise direction, a drive pulse of approximately 250milliseconds from pin 6 of timer U1 is applied to the gates of FETS Q8and Q9. Q8 is thereby turned on and supplies base current for transistorQ6. Collector current of transistor Q6 drives switch transistor Q1conductive, which is part of the current path for driving the motor in acounter clockwise direction. The drive pulse from pin 6 of timer U1 alsois applied to the gate of FET Q9 which turns on and provides drive toswitch transistor Q4 through R28 thereby turning on transistor Q4 which,along with Q1, controls the motor current in a counterclockwisedirection.

As mentioned previously, both the armature and field windings of themotor are individually connected and the direction of the motor isdetermined by the relative direction of current through these windings.In the arbitrary example illustrated, current reversal in one of thewindings makes the motor turn clockwise. When the current is in the samedirection in both windings, the motor turns in a counter clockwisedirection. The directional control is accomplished by connecting one ofthe windings M1 to the output terminals 82, 83 of rectifier bridge CR1.The current through that winding always flows in the same directionwhether drive current is received from switch transistors Q1 and Q4 orfrom switch transistors Q2 and Q3. Winding M2, on the other hand isconnected, in series with the input terminals 80, 81 of rectifier bridgeCR1, between the output terminals 72, 73 of switching bridge 57 andcurrent flow is reversed therein when the drive current is switched fromtransistors Q1, Q4 to transistors Q2, Q3. This was previouslyillustrated in FIG. 14. In the actual embodiment of the invention themotor is an AC motor that is operated with DC and the armature windingis connected to pins 1 and 4 of connector P2 and the field winding isconnected to pins 2 and 3 of the connector.

With the inventive torque limited module, the clutch elements areautomatically centered on the drive shaft and properly loaded by beingcontained within the upper and lower module plates and centering ring.Adjustment is neither provided, nor required, since the frictional forceis determined by the centering ring height, Belleville washers andfriction materials. As mentioned above, the spacer disc increases thesurface area of friction slippage and improves clutch performance. Thetorque limited module permits the motor to overrun after the breaker hasreached its limit of operating travel without the need for limitingswitches and reversing switches. The result is a very efficient andreliable motorized operator for a circuit breaker. The electricaloperator also does not require adjustment, which makes fieldinstallation a very simple task. In practice, the torque limited moduleis set to slip at 55 lb-ft to assure complete operation of the breaker.The motor drives the breaker through a single reduction gear, deliveringvery high torque in a very short period of time.

What has been described is a novel torque limited module that is easilyassembled and does not need adjustment. It is recognized that numerousmodifications and changes in the described embodiment of the inventionwill be apparent to those skilled in the art without departing from itstrue spirit and scope. The invention is to be limited only as defined inthe claims.

What is claimed is:
 1. A bidirectional torque limited assemblycomprising:a drive shaft adapted to be coupled to a driven member; gearwheel means rotably mounted on said drive shaft and adapted to becoupled to a drive gear; a torque limited module movable on said driveshaft with said gear wheel means; clutch means, having an outerdiameter, said clutch means including friction means having first andsecond friction discs separated by a spacer disc, pressure meansincluding a pair of Belleville washers and a drive plate, all mountedfor rotational movement on said drive shaft, in said torque limitedmodule, and being frictionally coupled to said drive shaft; means insaid torque limited module for aligning said clutch means on said driveshaft and within said torque limited module, said aligning meanscomprising a cylinder having an inner diameter that is slightly greaterthan said outer diameter of said clutch means; and wherein said torquelimited module includes first and second module plates, said firstmodule plate being drivingly coupled to said gear wheel and saidcylinder being sandwiched between said module plates, whereby frictionalloading of said clutch means on said drive shaft is predetermined andsubstantially constant.
 2. A bidirectional torque limited assemblycomprising:a drive shaft adapted to be coupled to a driven member; agear wheel rotatably mounted on said drive shaft and adapted to becoupled to a drive gear; a torque limited clutch module including: firstand second module plates, said first module plate being drivinglycoupled to said gear wheel; clutch means having an outer diameter andbeing frictionally coupled to said drive shaft and including frictionmeans, pressure means and a drive plate mounted for rotational movementon said drive shaft; and a cylinder having an inner diameter slightlygreater than said outer diameter of said clutch means, and beingsandwiched between said module plates for aligning said clutch means onsaid drive shaft and within said torque limited clutch module.
 3. Theclutch assembly of claim 2 wherein said pressure means includes a pairof Belleville washers and wherein said friction means includes first andsecond friction discs separated by a spacer disc.
 4. A bidirectionaltorque limited assembly comprising:a drive shaft adapted to be coupledto a drive member; gear wheel means rotatably mounted on said driveshaft and adapted to be coupled to a drive gear; and a preloaded torquelimited module including: first and second module plates; meansdrivingly coupling said first module plate to said drive shaft; frictionmeans coupling said drive shaft to said second module plate; a cylinderhousing said friction means; and means clamping said cylinder betweensaid first and second module plates.